A brief review of the use of near infrared spectroscopy with particular interest in resistance exercise.

Abstract

There is growing interest in resistance training, but many aspects related to this type of exercise are still not fully understood. Performance varies substantially depending on how resistance training variables are manipulated. Fatigue is a complex phenomenon usually attributed to central (neuronal) and/or peripheral (muscular) origin. Cerebral oxygenation may be associated with the decision to stop exercise, and muscle oxygenation may be related to resistance training responses. Near infrared spectroscopy (NIRS) is a non-invasive optical technique used to monitor cerebral and muscle oxygenation levels. The purpose of this review is to briefly describe the NIRS technique, validation and reliability, and its application in resistance exercise. NIRS-measured oxygenation in cerebral tissue has been validated against magnetic resonance imaging during motor tasks. In muscle tissue, NIRS-measured oxygenation was shown to be highly related to venous oxygen saturation and muscle oxidative rate was closely related to phosphocreatine resynthesis, measured by (31)P-magnetic resonance spectroscopy after exercise. The test-retest reliability of cerebral and muscle NIRS measurements have been established under a variety of experimental conditions, including static and dynamic exercise. Although NIRS has been used extensively to evaluate muscle oxygenation levels during aerobic exercise, only four studies have used this technique to examine these changes during typical resistance training exercises. Muscle oxygenation was influenced by different resistance exercise protocols depending on the load or duration of exercise, the number of sets and the muscle being monitored. NIRS is a promising, non-invasive technique that can be used to evaluate cerebral and muscle oxygenation levels simultaneously during exercise, thereby improving our understanding of the mechanisms influencing performance and fatigue.

But as practical users, we look at it ,as you can see fundemantally diffwerent. All current studies on strenght in combination with NIRS are looking just at the oxygenation information. As you can see in the summary above.

Muscle oxygenation was influenced by different resistance exercise protocols depending on the load or duration of exercise, the number of sets and the muscle being monitored.

This is absolutely true . What is missing is the information why the SmO2 reacted as it reacted. The reaosn why it is missing is the problem, that we look at SmO2 or O2Hb or HHb just form the utilization point of view. So justy because SmO2 drops does not help us to understand really for sure why. Is it really , that we use more than we deliver . Yes possibly, but it as well can be a shift in the O2 disscurve due to respiratory trends but even more important it can be due to very different delivery situations. 1. We may deliver perfect but it drops : Stable tHb but more O2 used than can be delivered but no problem with blood flow

or we may have a delivery problem so SmO2 is stable and tHb dropsOr we may have both more O2 use and as well drop in delivery of the blood. volume

Summary. When looking at SmO2 ( O2Hb or HHb trend alone we miss some crucial questions. Is it a sufficient blood delivery buy utilization outstrips delivery or is it in a extreme situation. ( not that extreme in strength training ) a simple delivery limitation due to occlusion and as such SmO2 drops as there is no additional delivery for the region. so it is NOT an underdelivery of available O 2 but simply no delivery due to occlusion. This has some fundamental different reactions , as in one case the delivery system may be limiting, in the other case the storage ability may be limiting the duration of the performance.

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